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By Thomas M. Barczak

The era of the shield-supported longwall face began in the United States a little over 25 years ago. The most fundamental development of the shield in the past 25 years has been an increase in size and capacity and a progression toward two-legged designs in favor over four-legged shields. Is the “bigger-the-better” design philosophy justified? The advantage of the two-legged design is largely attributed to its active horizontal force caused by the forward orientation of the leg cylinders. How do we know this? You might be surprised to learn that shield loading data may suggest otherwise. In addition, what about setting pressures? Should they be set as high as possible? Some people have advocated that setting pressures should equal the yield pressure. Does this make any sense? Is yielding a good or bad thing? These are some questions still worthy of investigation that are addressed in this paper. The first major change in gateroad support was the use of cable bolts to replace conventional wood cribbing particularly in Western mines. Standing support changed very little until the mid-1990s, when Strata Products1 introduced the Hercules and Propsetter supports in Eastern mines and Burrell Mining Products introduced the Can support in Western mines. Since then, there has been a dramatic increase in new roof support technologies for longwall gateroad support. Historically, standing support, including shield supports, have been designed based on a simplistic model requiring the support to have sufficient capacity to support the gravity loading of a perceived detached rock mass. This approach ignores the stiffness of the support and the resulting ground deformation that is known to be critical to roof stability. Recently, a new approach based on the ground reaction concept has been promoted by the National Institute for Occupational Safety and Health (NIOSH) to account for the interaction of the support with the rock mass behavior in achieving ground stability. In addition to gateroad support design, this concept has ramifications for shield capacities, setting pressures, and recovery room support design that challenge current practices in these areas. Although longwall mining has matured into the safest and most productive underground mining method used today, traditional concepts of roof support design and practice should still be evaluated and challenged. Ultimately, advancements in the science of ground control are made by recognizing deficiencies in current theories and thinking outside the box.

Scenario reduction is designed for selecting a representative subset of geostatistical simulations out of a much larger set. Three steps are involved: measuring the dissimilarity between two simulations; finding a metric to measure the distance between any subset of k simulations and the full set of N simulations; and finding an efficient algorithm for selecting the subset that minimizes the metric. This paper focuses on the third question. We show that genetic algorithms are an efficient way of approaching the minimum when the population of subsets to be sampled is large. Two case studies based on the Walker Lake data-set are presented: firstly choosing k=4 simulations out of a total of 100, and secondly choosing 20 out of the same 100 simulations. In the first case it was possible to compute all possible combinations exhaustively and hence to demonstrate that the algorithm converges to the true minimum. This was not possible in the second case. Instead we demonstrate that it outperforms the random draw algorithm used in earlier work. A procedure for tracking individual selections during the iterative procedure was developed. This allows us to measure the evolution in the percentage of progeny resulting from crossing-over and from mutation that survived in the next generation. It gives valuable insight into how to choose the parameter values in the algorithm. Another key finding is that there is a trade-off between the number of individuals per generation and the number of generations required for the algorithm to converge.

Jan 1, 2014

By R. Drummond

The fourth Teetered Bed Separator (TBS) has just been installed in Australia, and trials have been run in many sites. There is a growing recognition of the potential advantages of using TBS technology to treat coal in the ?3+0.25 mm size range, at cut points below 1.60. From these activities, there has been a substantial growth in knowledge with respect to application engineering and operational functions. The paper briefly describes the installations, including flowsheets, and so provides a background to the potential deployment of TBS technology. There are a large number of potential applications for TBS technology, including treatment of fine ROM coal in new plants, or in upgrade situations for re-processing of spiral product, or scavenging coal from coarse tailings. As well, cost effective capacity upgrades are possible by using TBS units for treating the sands size fraction. Issues arising from Australian TBS installations and application engineering are also discussed.

Jan 1, 2002

By E Lounejeva, J A Halpin, A Chappaz, D D. Gregory, S Wu, T Lyons, P J. Sack, R R. Large, S W. Bull

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. Newly published models suggest that some orogenic and Carlin-style gold deposits formed by the remobilisation of trace elements during interaction with hydrothermal or metamorphic fluids from early sedimentary pyrite that was enriched in Au, As and Te. The released trace elements are transported by the fluids to favourable trap sites where they are deposited. Therefore, early enrichment of Au, As and Te in source rocks (particularly in pyritic black shale) can be crucial to the formation of orogenic and Carlin-style gold deposits.The most important cause of the enrichment of gold and other trace elements in the sedimentary basins has been examined in this study to determine which basins are the most prospective for the development of orogenic gold deposits. An important influence for Au and other associated trace element accumulation in sedimentary pyrite is the temporal variation of trace element content in the oceans, as revealed by a database of over 1400 analyses of pyrite from black shale through geologic time. It is inferred that sediments coeval with those where sedimentary pyrite is enriched in Au and associated trace elements are more likely to be source rocks of orogenic and Carlin-style gold deposits.Factor analysis of the trace element content of pyrite through geologic time was conducted to investigate the multivariate relationships amongst trace elements and how these chemical factors explain the uptake of trace elements. One important factor includes Te, Au, Pb and Bi content. The incorporation of these large cations into pyrite is enhanced by As3+ substituting for Fe in pyrite lattice. The As3+ ion occurs in relatively oxidised environments and, thus, it is expected that shales deposited in non-euxinic waters are better source rocks for orogenic gold deposits.The examination of both the time in which the sediments were deposited and the redox conditions of the basin, and the ocean more broadly, can be used as a guide to approximate the extent of a basin’s fertility. To illustrate the use of this exploration tool, examples from the unmineralised Jet Rock Formation (UK) and the mineralised Castlemaine Group (Bendigo, Australia) are presented in this paper.CITATION:Gregory, D D, Large, R R, Halpin, J A, Lounejeva, E, Wu, S, Bull, S W, Sack, P J, Lyons, T and Chappaz, A, 2015. Accumulation of trace elements into black shale – how to identify a viable source rock for orogenic and Carlin-style gold deposits , in Proceedings PACRIM 2015 Congress, pp 59–64 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By Jeff Whyatt

Deformation of underground salt, trona and potash mines is generally time dependent, providing for gradual adjustment of strata to mining induced stresses. Time dependence can allow for higher extraction ratios provided eventual failure can be tolerated. However, this eventual failure can be violent if creep deformation can shift stress and potential energy to strong, brittle geologic units. The mine failure case studies reviewed here illustrate this process. Yield pillars and defects in bridging strata figure prominently in these cases. Yield pillars provide local and temporary support to the roof, temporarily delaying the cave; and allowing extraction ratios and overburden spans to increase beyond the long term capacity of overlying strata. Defects (faults, voids, thinning) of strong overburden strata reduce the critical span, sometimes to less than panel width. Analyses of many of these cases have focused on a cascading pillar failure mechanism, but recent work and this review point to failure of strong overburden strata as the essential element. The suddenness of failure and attendant seismic events pose hazards to miners and, in some cases, to those on the surface. Characterizing these failures is a first step towards recognizing and managing the risk of catastrophic collapse in underground mines.

Jan 1, 2008

By Hector Carreon

Due to elevated temperatures, excessive stresses and severed corrosion conditions, turbine engine components are subject to creep processes that limit the components life such as a turbine bucket. The failure mechanism of a turbine bucket is related primarily to creep and corrosion and secondarily to thermal fatigue. As a result, it is desirable to assess the current condition of such turbine component. By using eddy current images, it was shown that the eddy current technique could be used to monitor creep damage in a nickel base super-alloy. The eddy current results also show a significative variation in the electrical conductivity on the creep damage zone with respect to the background zone in nickel-base super-alloy samples. In addition, the absolute thermoelectric power coefficient show also a strong dependence associated with creep damage in nickel base super-alloy samples using a copper hot tip reference. The eddy current and thermoelectric power techniques seems to show promise as nondestructive evaluation tools for monitoring the level of creep damage in metallic alloys.

Jan 1, 2010

By James W. Weaver

The 2,120-foot long cable stayed Penobscot Narrows Bridge that carries US Route 1 over the Penobscot River between Verona Island and Prospect, Maine is supported on four foundation units, one below each pylon and one at each abutment. Due to varying subsurface conditions along the bridge alignment, the structure was designed to be supported on foundations consisting of high-capacity steel H-section piles (Verona Pylon), a mat bearing on a prepared bedrock surface (Prospect Pylon) and spread footings bearing on compacted rockfill (abutments). The 70-foot by 80-foot (plan area) Verona Pylon foundation was designed to be supported by 288, 430-kip design capacity steel H-section piles (HP14x117, 50 ksi steel) driven through up to 100 feet of dense glacial till deposits containing cobbles and boulders up to 3 feet in diameter. The piles were installed using a single-acting diesel hammer (Delmag D62-22) with a maximum rated energy of 165 kip-ft. Thirteen representative piles were selected for dynamic testing (ASTM D-4945) to verify pile capacity, hammer efficiency and pile stresses. Dynamic testing determined that four different pile driving criteria were needed across the site due to variation in the bedrock and soil resistance below the footing plan area. Approximately 4 percent of the production piles were damaged/rejected due to misalignment and/or damage as a result of encountering the cobbles and boulders embedded in the glacial till. The rejected piles were located randomly throughout the plan limits of the foundation mat. Subsequent structural analyses indicated that the foundation was capable of safely supporting the design loads without the need for installing replacement piles. Evaluation of dynamic testing results with signal matching and pile driving records provided valuable information on pile side and tip resistance. Evaluations were made regarding predicted versus actual pile lengths, pile bearing material, distribution of skin friction and end bearing capacities.

Jan 1, 2011

Silica reacts with cryolite at 1010°C in two stages. The first stage is the formation of a sodium aluminosilicate of composition consistent with the mineral jadeite (Na20.AI20s.4Si02). The formation proceeds by atleast two different reactions. Formation of alumina or an aluminosilicate proceeds to its limiting value in the first 30 min while the formation of jadeite proceeds at a steady rate until quantitative conversion is achieved after 150 min. The net overall reaction can be expressed by the equation 6 Si02+2 Na3AlF6? (Na20.AI20s.4Si02) +2 SiF4 +4NaF.The second stage involves a slow reaction that proceeds with the evolution of a little SiF4, The net result is the formation of sodium aluminosilicates that are soluble in 30 per cent AlCIs-HCI solutions. While this could be explained by disproportionation of jadeite to form albite (Na20.Al203.6Si02) and nepheline (Na20. AI203.2Si02), it is more likely that it is due to further but limited reaction between the oxides and fiuoroaluminates.

Jan 1, 1972

Minerals are fundamental to the U.S. economy, contributing to the real gross domestic product (GDP) at several levels?mining, processing and manufacturing finished products. The estimated growth rate for the real GDP of the United States was 2.1 percent and the nominal GDP was about $13.8 trillion in 2007 (Table 1). The prime interest rate decreased to 7.25 percent in December from 8.25 percent at the beginning of 2007, reflecting actions taken by the Federal Reserve Board to counter financial difficulties surrounding subprime mort-gages. Delinquencies on subprime mortgages increased throughout the year, affecting not only the delinquent home owners but also financial instruments invested in mortgage-backed securities. The average contract mortgage rate for the purchase of previously occupied homes in the United States was 6.35 percent in November; a slight decrease from 6.37 percent in January but still greater than 5.34 percent reported in July 2003, the lowest rate in the past five years. With the tightening of credit, the seasonally adjusted annualized rate for new privately owned housing starts declined 27 percent from December 2006 to November 2007. The loss in the residential market was balanced by a 9-percent increase in nonresidential construction between January and August 2007, during which slight increases occurred in nearly all

Jan 1, 2008

By Nils Heinke, Stephen M. Collinsorth

To anyone who is responsible for the production of blast holes, who is looked to on a daily basis for drill maintenance and performance, whose bottom line may depend on the survival of the mine itself.. How much awareness should one have on such things that truly impact production, maintenance and overall job cost? Do you know your drill’s maximum capacity?

Jan 1, 1998

By Giuliana A. Zelada-Tumialan

Reduced workability and flowability of the concrete through the tremie tubes and drilled shaft reinforcement have been identified as the main causes of tremie-concrete drilled shaft concrete defects. This paper discusses two recent case studies of defective tremie-concrete drilled shafts. The defects (soft inclusions, aggregate segregation, and low concrete strength) were primarily caused by the combined effects of the tremie placing sequence, rapid concrete slump loss, and poor passing and blocking characteristics of the approved concrete mix design. The level of detail contained in the drilled shaft specifications varied between projects. However, even when the specifications incorporated several of the more recent recommendations for tremie-concrete placement, the case studies showed that typical provisions for concrete mix proportioning and placement can be further improved to minimize construction defects such as those described in this paper. Based on the findings of the case studies presented, recommendations for the development of more effective specifications are provided. The recommendations include requirements for mock-up testing of proposed concrete mix designs and evaluation of the tremie-concrete placement sequence. Performance of such testing and evaluation would greatly reduce the potential for drilled shaft defects and consequent time and financial burdens associated with them.

Jan 1, 2009

By Philip Dubbeling

Conventional dynamic sheetpiling techniques are ill-suited to urban development because of the emission of excessive noise and ground vibrations. Drilled shafts and slurry walls alleviate some of these environmental concerns but add additional problems due to large bulky machines, reliance on dusty concrete plants and urban trucking grief. To solve these problems, pre-fabricated sheetpiles are hydraulically jacked-in by reaction principle using a compact and lightweight press-in machine, a so called the "Silent Piler". Through scientific analysis, definition and systemization of press-in machines and methods, new construction concepts such as the one-step approach, implant structures, functional design and life cycle design have been developed to comply with new basic construction principles.

Jan 1, 2006

By J Guo, K Williams, J Y. Guo, A W. Roberts, M Jones, B Chen

Numerical simulations using the discrete element method (DEM) were carried out to investigate the flow patterns and stress field redistribution at the hopper and feeder interface. The influences of different filling heights, belt speeds and clearances between the hopper bottom and feeder surface on feeder loads were studied. Meanwhile, experiments were conducted by utilising wedged plane-flow hoppers with different configurations and horizontal feeders with various clearances. The simulation results were compared with theoretical values and experimental measurements. In terms of the cases presented in this study, simulation results reveal good agreements with experimental observations regarding the flow pattern. Being similar to the theoretical values, the simulations provide close predictions on vertical feeder loads for steady flow states, but they may show significant overestimations for initial states. Additionally, suggestions are given for relevant simulation parameters based on the comparisons shown in this investigation.CITATION:Guo, J, Roberts, A W, Williams, K, Jones, M, Chen, B and Guo, Y J, 2017. Simulation investigation of flow patterns and feeder loads at hopper/feeder interface, in Proceedings Iron Ore 2017, pp 173–182 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 24, 2017

By D Crequer

A Peer Review Panel for the Golden Cross Mine in the upperWaitekauri Valley, Coromandel was initiated in December 1989, before mining, as a requirement of the conditions of the Mining Licence and Water Rights. The panel's function is as a technical audit and advisory team - to provide independent technical review of design, construction, and execution of mining operations, slope remediation works, and reclamation/mine closure activities. The primary role of the panel is to act in the public interest by providing assurance to regulating authorities that the design and application of on-site mining operations accords with 'good industry practice'. Panellists are not involved in design nor as advisers, although until 1997 when explicit terms of reference were written, the panellists were a sounding board for some operational proposals. The panel functions to ensure that best mining industry technical standards are met. The costs of the peer review process are met by the mining company. Review of mining operations includes environmental matters such as land rehabilitation and water quality. The focus of this paper is on the process of peer review for environmental management factors rather than for structural and mine engineering.

Jan 1, 1998

Authors have been conducting research on autonomous loading operation by wheel loader. Autonomous loading cycles has been demonstrated with real size experimental model. In V shape loading operation, travelling between scooping point and dumping point is dominant factor for cycle time of the operation. The positions of scooping point and dumping point changes with advancing the operation. In the developed system, path planning is performed at the beginning of every cycle. The path is formed by combination of curve and straight path elements. During travelling on the planned path, path following control is applied on the loader to keep position error in narrow range. Positioning of the loader is based on dead reckoning with correction by global positioning system (GPS) data. In a process of path following control, control value for steering angle is determined based on position error in lateral direction. Proposed method of path planning and position control is installed and tested in the real size experimental model. The detail and results will be described in the paper.

Dec 6, 2010

By Z. H. Zhou

It is difficult to remove cadmium from raw indium using only electrolytic refining because their standard potentials are similar. In this paper, physical and chemical methods were used to remove Cd from raw indium. Indium metal is vacuum refined for two hours at 400°C with a vacuum pressure of 20 Pa. In this process, 99.70% of the Cd can be removed. The removal rate of Cd reaches 90% to 95% when indium is further smelted for 10 minutes in a 20% glycerin solution of KI and I2 at 180°C. When pre-indium is electrolytic refined in an In2(SO4)3-H2SO4 system, in which the indium content is 80 to 100 g/L, the pH is 2.0-3.0 and the current density is 80 to 100 A/m2, the contents of the impurities decrease and the purity of the indium product reaches 99.99%.

Jan 1, 2007

By I. C. Edwards, G. E. Agar

INTRODUCTION Many research efforts over the past years have been devoted to the study of energy consumption in comminution and the characteristics of the broken material. The old "laws" have been superseded by more general methods of analysis1,2,3 but these methods have not received much attention outside the laboratory. The work to be described here was done in order to obtain scale-up information on wet rod milling of sylvinite. EXPERIMENTAL A 30 x 51 in. Denver rod mill with a scoop feeder was used for these tests. Ore was fed from a variable speed screw conveyor into the feed box along with saturated brine. The mill was filled to approximately 45% of its volume with 2400 lbs of a mixed rod charge. The minimum possible feed rate was 2.5 tph and the practical maximum for this mill was 8 tph. Individual tests were run by setting the solid feed rate, then adjusting the brine flow rate to give the desired pulp density. After steady state, as evidenced by constant discharge pulp density, had been reached, samples of the discharge were taken at 15-minute intervals. These samples were filtered, washed with alcohol, dried, then screened on Tyler screens using a Ro-tap shaker. The sylvinite feed was regular plant feed that had been scalped at 20 mesh and was tapped from the coarse ore bins. It had been previously passed through a roll crusher set at 3 inches and after scalping was essentially minus 1 in. plus 20 mesh. RESULTS The screen analysis of samples from each series of tests was plotted on double logarithmic scale paper to determine the reliability of the series. In some cases, a faulty sample or screening procedure dictated that the results of one test be discarded. The criterion is a simple one — if the slope of one plot was noticeably different from the others in the series, it was discarded. The only cases that caused difficulty were those in which the brine was not thoroughly displaced from the solids. When this occurred agglomerates were easily identified on the screens and the whole of the sample was retained on 3 or 4 screens. There were no border line cases. The number N given in Table 1 is the number of size analyses that were pooled to form the data shown in Fig. 1. While examining the reliability of the sizing and sampling by plotting the data, it became apparent that there was no significant difference between grinds made at 50 and 60% solids. For the analysis given here, these tests were regarded

Jan 1, 1967

By L. Hanschar, C. Bwalya, E. Mokola, K. Musonda, A. Makayi

This paper describes the installation, commissioning and operation of porous plugs featuring nitrogen gas purging in both Anode Furnaces at the Kansanshi Copper Smelter (KCS), a greenfield copper smelter which commenced operation in March 2015. The decision to install porous plugs was taken in November 2016 and the facilities were successfully commissioned on both anode furnaces in October 2017. The project was successful and has demonstrated the following process improvements: 12.2% reduction in main burner fuel consumption Larger average charge size, due to fewer accretions; 17 minute decrease in average refining cycle times Improvements in slag skimming operations Improved casting rates INTRODUCTION Porous plugs The application of porous plug technology in copper smelter anode furnaces is well established around the world. Vukovic and Gamweger (2017) and Wallner (2004) noted that the stirring and mixing action induced by the injection of inert nitrogen gas into the molten copper via porous plugs has potential benefits in the following areas: Homogenization of the temperature and composition of the molten copper resulting in Reduced fuel consumption Less tendency to overheat slag (reduced risk of refractory attack) Less slag produced with a lower degree of oxidation (lower rate of refractory wear) Less tendency for buildups to form Improved environmental performance (produce low sulphur blister at Peirce Smith converters) Elimination of buildups inside the furnace and potential for larger charges per cycle Reduced processing times and potential for shorter cycle times More efficient skimming of anode slag Shorter skimming time Less copper carry over to Peirce Smith converters Very little slag remaining in the furnace (reduced potential for buildups to form)

Jan 1, 2019

By Luis Martín Tejeda

La simulación numérica es considerada como uno de los mejores métodos de modelamiento y planeamiento en la evaluación de la estabilidad de los taludes en minería superficial. En ese sentido, el presente texto señala que a través del método de tensión-deformación, implementado en programas computacionales basados en el método numérico de elementos finitos, se puede llegar a localizar la probable superficie de ruptura. Asimismo, con los diferentes modelos constitutivos como el elástico perfectamente plástico, estos taludes pueden ser evaluados. Por último, se describe brevemente los mecanismos de ruptura en taludes altos, el cálculo del FS y algunas características del programa de elementos finitos PLAXIS v. 7.2.

Sep 19, 2006

By S. C. Tadolini

Roof support systems have evolved from standing posts and timbers to a generation termed ?big nails? where steel bars are inserted into boreholes and anchored with expansion shells and/or resin cartridges. These systems have been effective but are limited to mining height. Additionally, the properties of steel do not resists shear forces or have the flexibility being required in difficult ground conditions. The next generation of roof support systems is coupling the best parts of the ?big nail? and resin grouted cable bolt systems. This paper will present the advanced technical solutions of the next generation of cable systems that includes an indented high-capacity PC-strand used with a variety of fixtures. Case histories of support applications will be presented.

Jan 1, 2012